(1) Field of the Invention
The present invention relates to a method for producing a vaccine from a pathogenic bacterium. In particular, the present invention provides a method for producing a whole cell derived vaccine which has a broad spectrum of activity in producing immunity in a host against multiple serotypes of the bacterium, particularly in pigs.
(2) Prior Art
Most prior art bacterial vaccines are based upon killing a virulent strain of the bacteria by using formalin or by heat killing the bacteria. Generally the bacterial cells are a single serotype of the target bacteria. As a result, heterologous serotypes of the same bacteria can cause disease in spite of vaccination. The reason for this is not completely understood; however, it appears that antibodies to the heterologous serotype are not induced by the vaccine and thus there is no immunity.
Sonicating bacteria is also described by U.S. Pat. Nos. 3,862,313 to Fryer et al, 4,298,597 to Acres et al and U.S. Pat. No. 4,707,543 to Zollinger et al. In Fryer et al, the bacterial cells are formalin killed prior to sonication. Formalin treatment may alter bacterial components, making them less antigenic. Acres et al describe a vaccine prepared using multiple strains to produce the vaccine which is active against heterologous serotypes of the bacteria. The vaccine also contains cell fragments resulting from sonication or mechanical shearing. Zollinger et al describe an outer membrane complex which is isolated from the bacterium. The vaccines of the prior art have limited effectiveness against heterologous serotypes of a particular bacterium for which immunity is required.
Outer membranes (OM) have been used to produce vaccines. Proc. Int. Pig Veter. Soc. 10 81 (1988) by the present inventors describes an OM vaccine for pigs derived from Haemophilus pleuropneumoniae (now known as Actinobacillus pleuropneumoniae). The vaccine contained APP outer membranes. Such vaccines are effective. The OM were produced by sonication of lysozyme-sucrose treated cells and then sucrose density gradient centrifugation. The sonication was for 10-15 seconds. Lysozyme degrades peptidoglycan (cell wall). Sucrose maintains the cell membranes remaining after treatment with the lysozyme until the cells are sonicated. No preservative was used in the preparation of the vaccine. Sucrose density gradient centrifugation and separation of OM is not a commercially viable method for producing the vaccine.
There is a need for an improved method for commercially producing bacterial vaccines, particularly those effective against porcine contagious pleuropneumonia, caused by Actinobacillus pleuropneumoniae.